The present invention relates to semiconductor processing and, more particularly, to a system and method for monitoring characteristics of a moving substrate.
In the semiconductor industry, there is a continuing trend toward higher device densities. To achieve these higher densities, efforts continue toward scaling down device dimensions (e.g., at sub-micron levels) on semiconductor wafers. To accomplish such high device packing densities, smaller and smaller feature sizes are required. This may include the width and spacing of interconnecting lines, spacing and diameter of contact holes, and the surface geometry such as comers and edges of various features.
The process of manufacturing semiconductors, or integrated circuits, typically consists of more than a hundred steps, during which numerous of copies of an integrated circuit may be formed on a single wafer. Generally, the process involves creating several patterned layers on and into the substrate that ultimately form the complete integrated circuit. Fabricating a semiconductor using such sophisticated manufacturing techniques may involve a series of steps including cleaning, thermal oxidation or deposition, masking, etching, and doping.
Wafers may be pre-cleaned using, for example, high-purity, low-particle chemicals. Silicon wafers may be heated and exposed to ultra-pure oxygen in diffusion furnaces under carefully controlled conditions to form a silicon dioxide film of uniform thickness on the surface of the wafer.
A masking step is utilized to protect one area of the wafer while working on another area. This process typically includes photolithography or photo-masking. A photoresist or light-sensitive film is applied to the wafer, such as while supported in a suitable spin coating apparatus. A photoaligner aligns the wafer to a mask and then projects an intense light through the mask and through a series of reducing lenses, exposing the photoresist with the mask pattern.
The wafer is then xe2x80x9cdevelopedxe2x80x9d (the exposed photoresist is removed), such as by applying a developing solution while rotating the substrate on a suitable support. The developed substrate may then be thermally baked to harden the remaining photoresist pattern. It is then exposed to a chemical solution or plasma (gas discharge) so that areas not covered by the hardened photoresist may be etched away. The photoresist is removed using additional chemicals or plasma. In order to ensure correct image transfer from the mask to the top layer, various wafer inspection methodologies may be employed.
In a doping step, atoms with one less electron than silicon (e.g., boron), or one more electron than silicon (e.g., phosphorous), are introduced into the area exposed by the etching process to alter the electrical character of the silicon. These areas are called P-type (boron) or N-type (phosphorous) to reflect their conducting characteristics. The thermal oxidation, masking, etching and doping steps may be repeated several times until the last xe2x80x9cfront endxe2x80x9d layer is completed (e.g., all active devices have been formed).
Following completion of the xe2x80x9cfront end,xe2x80x9d a metalization process is implemented in which the individual devices are interconnected using a series of metal depositions and patterning steps of dielectric films (insulators). Semiconductor fabrication may include one or more metal layers separated by dielectric layers. Openings are etched in this film to allow access to the top layer of metal by electrical probes and wire bonds.
As device densities continue to improve, it becomes increasingly important in the semiconductor fabrication process to monitor feature characteristics at various stages of the process. In particular, it has become desirable to monitor characteristics while the substrate is moving, such as during fabrication (e.g., associated with a deposition, etching process, or the like).
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is intended to neither identify key or critical elements of the invention nor delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.
The present invention provides a system and method for monitoring characteristics of a substrate. A positioning system supports a substrate for movement. A measurement system emits a beam onto a moveable reflector, which reflects an incident beam to the substrate. The measurement system also detects a reflected and/or diffracted beam from the substrate. A control system controls movement of the reflector based on movement of the support to facilitate selective interrogation of the substrate.
In a particular aspect, the support moves the substrate (e.g., rotational movement) within a processing environment in which a desired material is applied to or removed from the substrate. The detected reflected and/or diffracted beam has optical properties indicative of substrate characteristics, such as thickness of a layer (or layers) of materials formed on the substrate. Accordingly, the application of materials onto the substrate and/or other process parameters can be controlled based on the optical properties of the reflected and/or diffracted beam.
Another aspect of the present invention provides a method for measuring characteristics of a substrate. The method includes moving a substrate supported within a processing environment. An incident light beam is emitted onto a reflector as the orientation of the reflector is adjusted based substrate movement so that the beam can selectively interrogate a surface of the substrate. Reflected and/or diffracted light is provided in response to interaction of the incident beam with the substrate, which reflected and/or diffracted light has optical properties indicative of substrate characteristics.